FACTORS THAT AFFECT THE ACCURACY OF RAMAN SHIFT MEASUREMENTS ON MULTICHANNEL SPECTROMETERS

Raman shift measurements have been made on cyclohexane, by using linea r interpolation between bracketing neon line positions to establish Ra man band wavelengths, Factors that affect the precision of these measu rements have been examined in detail. These include change of slit wid th, grating line spacing, neon line intensity, distance of separation of neon lines, and effects of small grating movements, All these have some effect, but the last factor is particularly important. Techniques that give standard deviations of 0.03 cm(-1) when measurements are ma de without moving the grating are degraded by about an order of magnit ude when the grating is moved. This result is attributed to adventitio us partitioning of signal power between adjacent detector elements. By deliberately moving the grating a small amount between otherwise repl icate measurements, one can control this effect, Values for the Raman shifts for eleven cyclohexane bands, based on approximately 800 Raman spectra and an equal number of neon emission spectra, are presented. T he values are compared with previous measurements. They are generally within the +/-sigma range of the earlier values, but the standard devi ations of these results are about an order of magnitude smaller.